PROJECT SUMMARY Cognitive Behavioral Therapy (CBT) is typically considered the current gold standard and first line treatment for disorders characterized by recurrent binge eating such as bulimia nervosa (BN) and binge eating disorder (BED). Outcomes, while clinically significant, leave substantial room for improvement with recent systematic reviews and meta-analyses finding that 40-50% of patients with BED and nearly 70% of patients with BN remain at least partially symptomatic after a full course of CBT. In an effort to improve outcomes, a growing number of researchers have begun to evaluate the use of mindfulness and acceptance-based behavioral treatments (MABTs) for BN and BED and preliminary evidence suggests such treatments can be effective for this population. Although the research on MABTs for binge eating remains nascent, MABTs are frequently used in clinical practice for BN and BED, with one recent study showing that patients are more likely to report that their therapist has used mindfulness-based techniques than CBT-specific techniques. Given the widespread clinical interest in MABTs and the growing body of research supporting the preliminary efficacy of these treatments, a fully powered tests of the efficacy, mechanisms of action, and moderators of outcome for MABT appears warranted. In particular, rather than testing any specific MABT treatment package (e.g. acceptance and commitment therapy, dialectical behavioral therapy, mindfulness-based eating interventions) in a large clinical trial, we believe that a study that can isolate and evaluate the independent and synergistic efficacy of the most commonly used MABT components has the highest potential for impact. A review of MABTs for BN and BED suggests that there are four commonly used MABT components: (1) Mindful Awareness, (2) Distress Tolerance, (3) Emotion Modulation, and (4) Values-Based Decision Making. MABT treatment packages have vary widely in which of these components they incorporated and which they emphasized. By identifying which components of MABTs are most effective (and for whom they are effective), we can emphasize the powerful elements of MABTs and deemphasize or eliminate inert components. A traditional RCT would not provide the power necessary to evaluate the independent and synergistic efficacies of four distinct treatment components compared to an active treatment approach such as CBT. Instead, the proposed study will use a Multiphasic Optimization Strategy (MOST) approach (including a full factorial design) in which 256 individuals with transdiagnostic binge eating pathology are assigned to one of sixteen behavioral treatments, i.e., representing each permutation of the MABT component described above being included or excluded from the base treatment (a version of CBT that emphasizes the key behavioral ingredients of this treatment approach). Results of the component analysis set up future work to evaluate an optimized treatment containing only effective components (which can be expected to have superior efficacy, efficiency and disseminability) against current gold-standard CBT.